Conventionally, there has been known a seam welding apparatus that holds welding targets (work pieces) between a pair of electrode rollers, and continuously welds the welding targets by rotating the electrode rollers while energizing the electrode rollers under pressure.
If the pressure onto the welding targets by the electrode rollers exceeds the allowable range, it will cause a bad influence on the work pieces, the electrode rollers, a robot that moves the seam welding apparatus, and the like. To cope with this, there is provided an equalizing mechanism having springs between the seam welding apparatus and the robot so as to bring the electrode rollers to follow the height of the work pieces (see Patent Literature 1, for example).
Accordingly, at the time of welding the work pieces, this mechanism prevents electrode chips from slipping on the work pieces, and excessive loads, such as bending forces and pressing forces, from being applied to the work pieces, or a shank and a pressurizing rod that support the electrode rollers from becoming bent. Therefore, the work pieces can be effectively protected, and welding operation can be preferably executed.